1. Field of the Invention
The present invention relates to a 2-4 cycle change-over engine and its control unit which perform 2 cycle running in the case of a low revolution of the engine and perform change-over into 4 cycle running in the case of a high revolution.
2. Description of the Prior Art
Ordinary engines are generally classified into the 2 cycle engine which performs steps of suction, compression, explosion and exhaust during 2 strokes of a piston which performs reciprocal movement that is one rotation of a crank shaft, and the 4 cycle engine which performs the above mentioned 4 steps during 4 strokes of a piston that is 2 rotations of a crank shaft.
And in the 2 cycle engine of the uniflow type, a suction port is arranged at a lower portion of a cylinder liner, suction and exhaust are performed at the same time with air sent by pressure during the descending stroke of the piston, and explosion is made very time when the crank shaft performs one revolution, so that rotational variation in an output shaft in less and a high torque can be generated, while in the 4 cycle engine, suction and exhaust are performed in independent strokes respectively, so that the energy consumption ratio is less as compared with the 2 cycle engine.
By the way, in case of running one engine with switching into the 2 cycle running or the 4 cycle running, there is the suction port for the case of 2 cycle running at the lower portion of the cylinder liner, so that there is such a problem that the interior of the cylinder communicates with the exterior when the piston performs the descending stroke during the 4 cycle running.
Thus, a means for closing the suction port at the lower portion may be provided during the 4 cycle running, however, when opening and closing of the suction port is dependent on the ascending and descending movement of the piston, there is limitation at an upper edge position of an opening portion of the suction port in order to provide a sufficient compression ratio, so that there is such a problem that the stroke cannot be made so large.
The present invention has been done taking such problems into consideration, an object of which is to provide a 2-4 cycle change-over engine and its control unit which can be easily switched into the 2 cycle running or the 4 cycle running in accordance with revolution of an engine in order to perform efficient running.